It has been so far known that a titanium dioxide thin film exhibits various functions through a photocatalytic reaction. It has been also known that the titanium dioxide thin film is formed on a surface of a substrate such as a metallic material, a semiconductor element, a plastic material or the like and is used as an antireflection material, a sensor material, an insulating material or the like. Further, as a method for forming a titanium dioxide thin film on the surface of such a substrate, a coating method, a dipping method, a sputtering method and a CVD method in which a metallic heat-evaporated vapor is introduced into an oxygen gas atmosphere for reaction have been known.
Of these conventional methods for forming a titanium dioxide thin film, the coating method and the dipping method cannot form a titanium dioxide crystalline orientation film, and the sputtering method can hardly control the crystal structure of the thin film obtained. In the conventional CVD method, in order to form a crystalline titanium oxide thin film on a surface of a substrate, it was required that a substrate is usually heated at a high temperature of from 500 to 800.degree. C. and the formation of the thin film is conducted under reduced pressure in a closed plating chamber. In this conventional CVD method, the deposition rate of the titanium dioxide thin film was quite low, and the crystal structure of the thin film obtained was hardly controlled, making it impossible to obtain a crystalline orientation film oriented in a specific direction.